AP Bio 2.5 Membrane Permeability
41 flashcards covering AP Bio 2.5 Membrane Permeability for the AP-BIOLOGY Unit 2 section.
Membrane permeability is a key concept in AP Biology that explores how substances move across cellular membranes. Defined by the College Board in the AP Biology Curriculum Framework, this topic covers the mechanisms of transport, including passive and active transport, and the factors that influence permeability, such as membrane structure and concentration gradients. Understanding these principles is essential for grasping cellular function and homeostasis.
On practice exams, questions about membrane permeability often include scenarios requiring the application of concepts to predict the movement of molecules across membranes. Common question styles include multiple-choice and free-response formats, where students must analyze graphs or experimental data. A frequent pitfall is misunderstanding the distinction between passive and active transport, leading to incorrect assumptions about energy requirements and directionality of movement.
One concrete tip is to always consider the size and polarity of molecules when predicting their permeability across membranes, as this can significantly affect their transport mechanisms.
Terms (41)
- 01
What is membrane permeability?
Membrane permeability refers to the ability of a membrane to allow substances to pass through it, which can be influenced by factors such as the size, charge, and polarity of the molecules.
For instance, small nonpolar molecules can easily diffuse through the lipid bilayer.
- 02
Which factors affect membrane permeability?
Factors that affect membrane permeability include lipid composition, temperature, and the presence of proteins such as channels and carriers in the membrane.
Higher temperatures can increase membrane fluidity, enhancing permeability.
- 03
What is the role of cholesterol in membrane permeability?
Cholesterol helps to stabilize membrane fluidity, making the membrane less permeable to very small water-soluble molecules that might otherwise pass freely through.
In animal cells, cholesterol maintains membrane integrity at varying temperatures.
- 04
How does temperature influence membrane permeability?
As temperature increases, membrane fluidity typically increases, which can enhance permeability to certain substances.
At higher temperatures, phospholipids move more freely, allowing for greater diffusion rates.
- 05
What is facilitated diffusion?
Facilitated diffusion is a process where substances move across a membrane with the help of transport proteins, without the expenditure of energy.
Glucose transport into cells occurs via facilitated diffusion through specific glucose transporters.
- 06
What is the difference between passive and active transport?
Passive transport does not require energy and moves substances down their concentration gradient, while active transport requires energy to move substances against their gradient.
Sodium-potassium pumps are an example of active transport.
- 07
What is osmosis?
Osmosis is the diffusion of water across a selectively permeable membrane, moving from an area of lower solute concentration to an area of higher solute concentration.
Plant roots absorb water from the soil through osmosis.
- 08
How does the concentration gradient affect diffusion?
The concentration gradient affects diffusion by determining the direction and rate at which molecules will move; substances move from areas of high concentration to low concentration until equilibrium is reached.
If a dye is added to water, it will diffuse from the concentrated area to the less concentrated areas.
- 09
What is a selectively permeable membrane?
A selectively permeable membrane allows certain molecules or ions to pass through while restricting others, crucial for maintaining cellular homeostasis.
Cell membranes are selectively permeable, allowing nutrients in while keeping toxins out.
- 10
How does size affect membrane permeability?
Generally, smaller molecules can pass through membranes more easily than larger molecules, which may require specific transport mechanisms.
Oxygen and carbon dioxide can diffuse freely across the membrane due to their small size.
- 11
What type of molecules can easily cross the lipid bilayer?
Small nonpolar molecules, such as oxygen and carbon dioxide, can easily cross the lipid bilayer due to their solubility in the hydrophobic core of the membrane.
Gases like oxygen diffuse rapidly into cells for respiration.
- 12
What is the significance of membrane proteins in permeability?
Membrane proteins play critical roles in transport and signaling, facilitating the movement of substances that cannot diffuse freely across the lipid bilayer.
Aquaporins are channel proteins that facilitate water transport across cell membranes.
- 13
What is the function of aquaporins?
Aquaporins are specialized channel proteins that facilitate the rapid transport of water across cell membranes, enhancing membrane permeability to water.
Kidney cells use aquaporins to regulate water reabsorption.
- 14
How does pH affect membrane permeability?
pH can influence the charge and solubility of molecules, affecting their ability to cross the membrane; charged molecules may find it more difficult to pass through.
Acidic or basic conditions can alter the ionization state of molecules.
- 15
What is active transport?
Active transport is the process of moving substances across a membrane against their concentration gradient, requiring energy, typically in the form of ATP.
The sodium-potassium pump actively transports sodium out of and potassium into the cell.
- 16
What is bulk transport?
Bulk transport, or vesicular transport, involves the movement of large particles or volumes of substances into or out of cells via vesicles, which requires energy.
Endocytosis allows cells to take in large molecules or particles.
- 17
What is endocytosis?
Endocytosis is the process by which cells engulf external substances, bringing them into the cell enclosed in a vesicle, requiring energy.
Phagocytosis is a type of endocytosis where cells ingest large particles.
- 18
What is exocytosis?
Exocytosis is the process where cells expel materials in vesicles that fuse with the plasma membrane, releasing their contents outside the cell, requiring energy.
Neurotransmitters are released from neurons via exocytosis.
- 19
How does the presence of transport proteins affect membrane permeability?
Transport proteins increase membrane permeability by providing specific pathways for certain molecules to cross the membrane that would otherwise be impermeable.
Glucose transporters allow glucose to enter cells more efficiently.
- 20
What is the role of membrane fluidity in permeability?
Membrane fluidity affects how easily substances can move within the membrane and across it; more fluid membranes allow for greater permeability.
Increased fluidity at higher temperatures enhances the diffusion of lipids and proteins.
- 21
What is the role of the sodium-potassium pump?
The sodium-potassium pump is an active transport mechanism that maintains the electrochemical gradient by pumping sodium out of and potassium into the cell, crucial for cell function.
This pump is vital for nerve impulse transmission.
- 22
What happens to cells in a hypertonic solution?
In a hypertonic solution, water moves out of the cell, causing it to shrink due to a higher solute concentration outside than inside the cell.
Plant cells lose turgor pressure and wilt in hypertonic environments.
- 23
What happens to cells in a hypotonic solution?
In a hypotonic solution, water moves into the cell, leading to swelling and potentially bursting due to a lower solute concentration outside than inside the cell.
Red blood cells can lyse in pure water.
- 24
What is the role of carrier proteins in membrane transport?
Carrier proteins facilitate the transport of specific molecules across the membrane by changing shape to move the substance from one side to the other, often involved in facilitated diffusion.
Glucose is transported into cells via a specific carrier protein.
- 25
What is the significance of membrane potential?
Membrane potential is the voltage difference across a membrane, crucial for processes like nerve impulse transmission and muscle contraction, influenced by ion distribution.
Resting membrane potential is essential for neuron function.
- 26
How does the structure of phospholipids contribute to membrane permeability?
The amphipathic nature of phospholipids, with hydrophilic heads and hydrophobic tails, creates a bilayer that selectively allows certain substances to pass while blocking others.
This structure is fundamental to the fluid mosaic model of membranes.
- 27
What is the fluid mosaic model?
The fluid mosaic model describes the cell membrane as a dynamic structure with various proteins floating in or on the fluid lipid bilayer, contributing to its permeability and functionality.
Proteins in the membrane can move laterally, allowing for cellular signaling.
- 28
How do ion channels function in membrane permeability?
Ion channels are integral membrane proteins that allow specific ions to pass through the membrane, often gated by voltage or ligands, facilitating rapid changes in membrane potential.
Voltage-gated sodium channels open during an action potential.
- 29
What is the effect of solute concentration on diffusion rates?
Higher solute concentrations typically increase the rate of diffusion until equilibrium is reached, as molecules move from areas of high to low concentration.
The rate of dye diffusion in water is faster at higher concentrations.
- 30
What is the significance of membrane receptors in cell signaling?
Membrane receptors bind specific molecules (ligands) and initiate cellular responses, affecting membrane permeability and other functions.
Insulin receptors facilitate glucose uptake in response to insulin.
- 31
How do temperature changes affect membrane fluidity?
Temperature changes can increase or decrease membrane fluidity; higher temperatures generally increase fluidity, while lower temperatures decrease it, affecting permeability.
Cold temperatures can solidify membranes, reducing permeability.
- 32
What is the role of glycoproteins in cell membranes?
Glycoproteins serve as recognition sites on cell membranes, playing a role in cell-cell interactions and signaling, which can influence permeability.
Cell recognition in the immune response is mediated by glycoproteins.
- 33
How does the presence of unsaturated fatty acids affect membrane permeability?
Membranes with unsaturated fatty acids have kinks that prevent tight packing, increasing fluidity and permeability compared to saturated fatty acids.
Plant cell membranes often contain more unsaturated fats for flexibility.
- 34
What is the impact of membrane composition on permeability?
The composition of a membrane, including the types of lipids and proteins present, directly affects its permeability to various substances.
Membranes rich in cholesterol are less permeable to small polar molecules.
- 35
What is the difference between simple diffusion and facilitated diffusion?
Simple diffusion involves the direct movement of molecules across the membrane without assistance, while facilitated diffusion requires specific transport proteins to assist the process.
Oxygen diffuses directly, while glucose requires a transporter.
- 36
What is the role of receptor-mediated endocytosis?
Receptor-mediated endocytosis is a selective process where cells take in specific molecules after they bind to receptors on the cell surface, enhancing efficiency in nutrient uptake.
Cholesterol is taken up by cells through this mechanism.
- 37
How do environmental factors influence membrane permeability?
Environmental factors such as temperature, pH, and solute concentration can significantly alter the permeability of membranes by affecting fluidity and protein function.
Extreme pH levels can denature membrane proteins, affecting transport.
- 38
What is the importance of membrane permeability in homeostasis?
Membrane permeability is crucial for maintaining homeostasis by regulating the entry and exit of substances, ensuring the cell's internal environment remains stable.
Cells regulate ion concentrations to maintain osmotic balance.
- 39
How does the presence of integral proteins affect membrane function?
Integral proteins span the membrane and play key roles in transport, acting as channels or carriers, thus directly influencing membrane permeability.
Integral proteins facilitate the movement of ions and larger molecules.
- 40
What is the significance of membrane asymmetry?
Membrane asymmetry refers to the differing compositions of the inner and outer leaflets of the membrane, which can affect permeability and functionality.
Phospholipids and proteins are distributed unevenly, impacting cell signaling.
- 41
How does cell size affect membrane permeability?
Smaller cells typically have a higher surface area-to-volume ratio, which can enhance their ability to exchange materials across the membrane more efficiently than larger cells.
Bacteria are generally more efficient at nutrient uptake due to their small size.